1. Field of the Invention
The present invention relates to a photo film cassette and a cassette containing case for the same. More particularly, the present invention relates to a photo film cassette of which a cassette shell consists of a pair of shell halves secured to one another via engagement of claws, a cassette containing case for the same.
2. Description Related to the Prior Art
There is an IX240 type of photo film cassette, in which a photo film including its leader is pre-contained in a cassette shell, and the leader of the photo film is advanced to the outside when a spool is rotated. U.S. Pat. No. 5,476,232 (corresponding to JP-A 6-266053) discloses a construction of the cassette shell in combination of a pair of shell halves of resin. There is a first arm formed on one of the shell halves and protruded inwards for retention. A second arm is formed on the other of the shell halves and protruded outwards for receiving the retention. The first arm is engaged with the second arm in a snap connection to join the shell halves fixedly. There are two retainer mechanisms each of which includes the first and second arms, and which are located in respective lateral positions beside a photo film passageway through which the photo film is passed. The first and second arms have such a sufficient width in a direction of an exit slot of the passageway that lateral ends of the passageway is enclosed in a reliably light-tight manner.
There is a problem in the simple snap connection as described in the prior art portion of U.S. Pat. No. 5,647,552 (corresponding to JP-A 8-146561). The photo film cassette was subjected to a test of dropping down to an iron plate from a height of 2 (two) meters. A considerable number of sample cassettes resulted in disengagement of the snap connection. U.S. Pat. No. 5,647,552 suggests an idea of reinforcing the snap connection. The second arm is constituted by a second claw protruded outwards and an engaging face or recessed face. The second claw prevents the first arm from being disengaged. The engaging face receives a first claw protruded inwards from the first arm. The first arm is formed in such a size that, when the first arm is fitted at the engaging face, the first claw and the engaging face are pressed against each other. To form the first arm, the same document discloses relevant values, including: a height of the first claw of the first arm, a shifting amount at which the first arm is shifted for passing by the second claw, and a sectional area of an erected support supporting the first claw of the first arm for the purpose of maintaining the shifted amount thus determined.
However there occurs a problem of play between the first and second arms or failure in the retention between them, because a height of the second arm is not determined suitably. If heights of the first and second arms are determined, dimensional tolerances are provided for the heights. The shell halves are molded by respective separate molds. When shell halves are combined randomly, deviations in the ranges of the dimensional tolerances becomes dimensional errors. Of course it is conceivable to reduce such dimensional errors. Then another problem arises in narrowing ranges of the dimensional tolerances, and increasing costs of production by use of molds.